Gas cylinders are widely used in medical and industrial settings for the dispensing of compressed liquefied gas such as nitrous oxide or carbon dioxide, etc. In a compressed liquefied state, certain gases (e.g. nitrous oxide or carbon dioxide, etc.) exist in the cylinder in two phases, namely liquid phase and gas phase. In this two phase state, the gas pressure of the system is generally dependent on the temperature and independent of the liquid volume in the cylinder. During usage of the cylinder, there will come a time when the liquid within the cylinder is consumed. At this point, the remaining gas pressure in the cylinder is dependent on gas volume such that as the volume of gas within the cylinder decreases so does the pressure. Compressed gas cylinders typically include a mechanical or electronic manometer to alert the user as to the pressure of the compressed gas within the cylinder and thus the volume of remaining gas within the cylinder. Such mechanical or electronic manometers are of little use when the contents of the cylinder are a compressed liquefied gas or two phase fluid.
Users of a compressed liquefied gas need to know the contents of the containment vessel and when the contents are nearing or at a depleted condition. Prior art systems used to monitor compressed liquefied gases or two phase fluids would employ liquid level measurement technologies to accurately determine the compressed liquefied gas contents of such cylinders. Unfortunately, such liquid level measurement technologies are more costly and complex than the standard mechanical or electronic manometers, and often dependent of the orientation of the cylinder or vessel. Thus, there is an ongoing need to provide a simple, inexpensive apparatus that alert users of a compressed liquefied gas to when the contents of the cylinder are nearing or at a depleted condition.